[CIR] Make UndefAttr use AttrBuilderWithInferredContext (#136605)

This mirrors incubator changes from llvm/clangir#1577

Author: xlauko

clang/include/clang/CIR/Dialect/IR/CIRAttrs.td

@@ -93,6 +93,13 @@ def UndefAttr : CIR_Attr<"Undef", "undef", [TypedAttrInterface]> {
   }];
 
   let parameters = (ins AttributeSelfTypeParameter<"">:$type);
+
+  let builders = [
+    AttrBuilderWithInferredContext<(ins "mlir::Type":$type), [{
+      return $_get(type.getContext(), type);
+    }]>
+  ];
+
   let assemblyFormat = [{}];
 }
 

clang/lib/CIR/Dialect/IR/CIRMemorySlot.cpp

@@ -34,8 +34,8 @@ llvm::SmallVector<MemorySlot> cir::AllocaOp::getPromotableSlots() {
 
 Value cir::AllocaOp::getDefaultValue(const MemorySlot &slot,
                                      OpBuilder &builder) {
-  return builder.create<cir::ConstantOp>(
-      getLoc(), slot.elemType, builder.getAttr<cir::UndefAttr>(slot.elemType));
+  return builder.create<cir::ConstantOp>(getLoc(), slot.elemType,
+                                         cir::UndefAttr::get(slot.elemType));
 }
 
 void cir::AllocaOp::handleBlockArgument(const MemorySlot &slot,